Pull up to a petrol pump and you are immediately presented with three fuel octane ratings: 91, 95 and 98.
Many times you’d pump 95, thinking it’s a good compromise between the “low-grade” 91 and the rocket fuel 98.
Some drivers only put 98 into their car as they feel it needs the best to perform, but that’s not the smartest choice.
What does your car really require?
What do the numbers mean?
Here’s a cheat sheet: “standard” unleaded is 91, while premium fuels are 95 and 98.
Some countries even go further by providing E10 or E85 ethanol-based fuels, which are derived from sugarcane and are cheaper than 91.
These numbers – 91, 95, 98 – are in fact octane ratings.
Contrary to popular belief, pumping a higher fuel number into your car doesn’t actually make it go faster – all have about the same energy.
Instead, the numbers are an arbitrary index of the fuel’s resistance to burning – or detonating – too early in your engine.
If fuel burns too early in your engine, knocking or ‘pinging’ can occur, which can damage or even destroy engines.
Automakers design for a particular rating, and so you must check which grade is suitable for your car.
What octane rating is my car?
First thing to do is check what the fuel flap of your car says.
If it says ‘unleaded petrol only’ then you are safe to use any of the octane ratings.
If your fuel flap says ‘premium unleaded only’ then you must pump at least 95. If it actually specifies a grade, follow it.
Please make sure you check your car’s manual for the correct grade of fuel to use.
Cars designed for higher octane ratings cannot run on lower-rated fuels – it could be destructive to the engine.
Most modern cars (anything made past 2000) have knock sensors which detect the compression detonation and delays the spark to minimise knocking or pinging.
This is good for protecting the engine from pre-ignition knocking.
But in high-performance cars, the delay in the spark delay produces less power and gives you worse fuel economy.
If you pump a higher grade of fuel than necessary, it’s only a good thing for your car but probably not your wallet.
You could possibly get better fuel economy from pumping a higher grade, as well as a cleaner engine (injectors).
However, the price difference from 95 to 98 will make most drivers think twice about paying more.